Sunday, April 1, 2012

IC LM338 Application Circuits - Explained in Simple Words

The IC LM338 by TEXAS INSTRUMENTS, is a versatile IC which can be wired in numerous different ways for obtaining high quality power supply circuit configuartions.
The following circuit examples simply depict few of the very interesting useful power supply circuits using this IC.

Let's study each circuit diagram in details:

Simple Adjustable Voltage Power Supply Circuit

The first circuit shows the typical wiring format done around the IC. The circuit provides an adjustable output right from 1.25V to the maximum applied input voltage which shouldn't be more than 35 vots.

R2 is used for varying the output voltage continuously.

Simple 5 Amp Regulated Power Supply Circuit

This circuit produces an output that may be equal to the input supply voltage but the current is well regulated and can never exceed the 5 Amp mark. R1 is precisely selected so as to maintain a safe 5 amp maximum current limit that can be withdrawn from the circuit.

15 Amp, Variable Voltage Regulator Circuit

The IC LM 338 alone is specified for handling a maximum of 5 Amp of current, however if the IC is needed to handle higher currents, in the region of 15 amps, it can well be modified to produce that much of current with the appropriate modifications as shown below. The circuit utilizes three IC LM338 for the intended implementations with output voltage that's adjustable as explained for the first circuit. R8 is used for the voltage adjustment operations.

Digitally Adjustable Power Supply Circuit:

In the above designs, the power supply utilized a pot for implementing the voltage adjustment procedure, the below given design incorporates discrete transistors which can be digitally triggered separately for obtaining the relevant voltage levels at the outputs. The collector resistance values are chosen in an incremental order so that a correspondingly varying voltages can be selected and becomes available through the external triggers.

Light Controller Circuit

Other than power supplies, LM338 can also be used as a light controller. The circuit shows a very simple design where a phototransistor replaces the resistor which normally acts as the component for adjusting the output voltage. The light which needs to be controlled is powered by the output of the IC and its light is allowed to fall on this phototransistor. As the light increases the value of the photo-transistor decreases which in turn pulls the ADJ pin of the IC more toward the ground, forcing the output voltage to decrease which also decreases the light illumination, maintaining a constant glow on the lamp.

Current Controlled Power Supply Citcuit:

The next circuit shows a super simple wiring with the IC LM338 whose ADJ pin is connected to the output after a current sensing preset. The value of the preset determines the maximum amount of current that becomes permissible through the IC at the output.

12V Current Controlled Battery Charger Circuit

The circuit below can be used to charge a 12 volt lead acid battery safely. The resistor Rs may be selected appropriately for determining the desired level of current for the connected battery. R2 can be adjusted for obtaining other voltages for charging other categories of batteris.

Slow Turn ON Output Power Supply

Some sensitive electronic circuits require a slow start rather than the usual instant start. The inclusion of C1 makes it sure that the output from the circuit rises gradually to the set maximum level ensuring the intended safety to the connected circuit.

Heater Controller Circuit

IC LM338 can also be configured for controlling temperature of a certain parameter like a heater. Another important IC LM334 is used as the sensor which is connected across the ADJ and ground of the IC LM338. If the heat from the source tends to increase above the predetermined threshold, the sensor lowers its resistance correspondingly, forcing the output voltage of LM338 to fall, subsequently decreasing the voltage to the heater element.

10 Amp Regulated Power Supply Circuit

The following circuit shows another circuit whose current is restricted to 10 amps, that means the output can be made suitable for high current rated loads, the voltage is adjustable as usual via the pot R2.

Adjusting Many LM338 modules via a Single Control

The given circuit shows a simple configuration which can be used for controlling the outputs of many LM338 power supply modules simultaneously though a single pot.

prashant, 78XX ICs are internally short circuit protected, they will never get shorted unless tampered intentionally. Even if this happen, the cell phone is protected against upto 12V supplies and will simply show"not charging"

good day sir. i wat to build a powersupply with lm338 but i want to be able to adjust the curent to not just the voltage i saw a schematic above with a simple curent limiting circuit.but if i make that circuit how can i adjust the voltage not just the curent?

Hello sir, I'd like to know how to charge a 12V7Ah lead gel-acid battery, I know that the "slow charge" must me 700mA, so I have to supply the battery with 700mA, and I don't know how to calculate the external components. Thank you very much for the help beforehand

hello Jeronimo, you can build the first circuit from the above article exactly as shown, just replace the pot with a 10k pot.... for setting up the circuit adjust the pot to get around 14V at the output without any battery connected. once this setting is done connect the battery and switch ON power...let it charge for about 8 hours and then you could switch OFF the supply manually, you would find the battery fully charged by this time.

Please Share!

You all are Awesome

About Me

I am an electronic hobbyist, inventor, a freelance electronic circuit designer, manufacturer. I am also an avid publisher, I enjoy posting electronic related articles in my website: http://www.homemade-circuits.com/ where the interested viewers get the opportunity to read about many innovative electronic circuit ideas, exclusively designed and developed by me.